Thin film magnetic recording media are major elements of hard disk drives which are widely used in computers and other data storage devices. As the recording density continues to increase towards the next goal of 10 Gbit/in.sup.2 and beyond, more efforts are being made to enhance media coercivity and to reduce noise. In addition to improving media alloys and structures, alternative substrates such as glass and glass-ceramic are found to be more suitable than the traditional NiP-plated aluminum (NiP/Al) substrates. Some of the advantages of using these alternative substrates include lower media noise and lower flight height which could lead to higher recording density. Moreover, these alternative substrates can access to higher temperatures without disk warping that usually happens with NiP/Al at high temperatures. The superior mechanical properties of such alternative substrates also make it possible to reduce disk thickness and size.
To obtain high quality media films, it is necessary to apply dc bias during the film deposition process. However, the dielectric nature of non-metallic substrates causes difficulties in applying dc bias. Moreover, the fast heat loss rate of most non-metallic substrates makes it difficult to sustain the high temperature required for preferred orientation of media films. Consequently, media deposited directly on non-metallic substrates usually exhibit low coercivity and poor recording performance. In order to improve the coercivity, an extra thin metallic seedlayer/sublayer film is needed between the non-metallic substrate and media films. It provides not only the electric conductivity necessary for applying dc bias, but also better growth conditions for the subsequently deposited media films.
Since the optimum deposition process for a seedlayer/sublayer is mainly a sputtering--PVD (Physical Vapor Deposition) process, the sputtering targets of these materials play a very critical role in the guarantee of the sublayer performance and the magnetic media recording layer performance. In addition to the other controlling factors, sputtering targets must be carefully engineered with designed chemistry, composition and purity. Moreover, optimum microstructure and other controlled characteristics must be properly controlled with advanced manufacturing metallurgical processes, otherwise the demanded recording performance of hard disks cannot be achieved.
Advanced metallurgical processes for the manufacturing of high performance targets include hot hydraulic pressing, hot isostatic pressing (HIP), cold isostatic pressing (CIP), and melting.